They must have a host cell
in order to survive. They enter
the cell andtake over the
hostís metabolic machinery to
make more of themselves.

Viruses can infect a wide range
of hosts or type of tissues, or
have alimited affinity for
some of them. This is called
species, host, or tissue
specificity and depends on the
host cellís receptors and the
viral spikes orpeplomers (a
specific key opens only a
specific lock concept).

Some viruses can remain
latent or produce a chronic
infection in the host,some
others are potentially oncogenic
or Teratogenic (have the ability
toinduce carcinogenic or
mutagenic changes in the host
genome), and stillother can
produce mild to fatal diseases
in the host.

Viruses that
infect and cause disease in
humans are divided into two
largegroups based on the
type of their genetic material,
either DNA or RNA.

Only
animal viruses show an
additional layer covering the
capsid calledenvelope.
Enveloped viruses are less
resistant to disinfectants,
heat, etc.than their naked
counterparts.
Polymerase Chain Reaction PCR to
detect virus effects in DNA

Thepolymerase chain
reaction is a technique to
amplify a single or few copies
of a piece of DNA across several
orders of magnitude, generating
thousands to millions of copies
of a particular DNA sequence
Polymerase Chain Reaction is a
sensitive technique to
locate tiny fragments of virus
DNA .

Interferons

Host
cells have several defenses
against the viral attacks. For
example viral infection leads to
the synthesis and secretion of
proteins called interferons ,
which "interfere" with viral
replication by helping adjacent
uninfected cells become
resistant to infection.